power dissipation - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 27th February 2002, 09:06 PM   #1
diyAudio Member
 
Join Date: Oct 2001
Location: UW Stevens Point Campus
Default power dissipation

How would a person calculate the power dissipation for a given power level?

newbie question, yeah I know

Opie
  Reply With Quote
Old 27th February 2002, 11:15 PM   #2
haldor is offline haldor  United States
diyAudio Member
 
Join Date: Aug 2001
Location: Columbus, Ohio
Power dissipation is the voltage drop across a device multiplied times the current flowing through the device. This is true for passive components (like resistors) and active components (like voltage regulators and transistors).

Example:

+5 VDC fixed linear regulator. Supply voltage = 12 VDC. Current flow through device = 0.1 A.

Voltage drop accross device will be 12 VDC - 5 VDC = 7 VDC
Dissipation = 7 VDC X 0.1 Amps = 0.7 Watts

Phil
  Reply With Quote
Old 28th February 2002, 01:33 AM   #3
diyAudio Member
 
Join Date: Oct 2001
Location: UW Stevens Point Campus
haldor,
I am building the holton n-channel amp and I wish to calculate the power dissipation with supply rails of 84 volt dc rails. Will there be a voltage drop when the supply is loaded? I am guessing that the amp will put out 500-600 watts into 4 ohm. Is the correct so far?

Thank you,

Opie
  Reply With Quote
Old 28th February 2002, 01:58 AM   #4
Warp Engineer
On Holiday
 
AudioFreak's Avatar
 
Join Date: Oct 2001
Location: Queensland, Australia
Opie,

Yes because the power supply and the mains wiring have a finite resistance, there will be a voltage drop @ full load.... how much depends on all these series resistances.

well power into any ohmage can be calculated thusly ....

(VxV)/(Rx2)=RMS Power

Where V = the supply voltage and R = the load resistance of the speaker.

Now assuming no voltage drop the following would be true....

(84x84)/(4x2) = 882W RMS

But this would probably drop to around 650W or maybe lower depending on the factors listed above. Also, you must ensure that all devices are kept within their SOA to minimize device failures and therefore, further derating of output power maybe required to satisfactorily achieve this.
  Reply With Quote
Old 28th February 2002, 02:09 AM   #5
diyAudio Member
 
Join Date: Oct 2001
Location: UW Stevens Point Campus
Audiofreak,

I am planning on using IRFP260N hexfets in the output stage, they have a max operating temp of 175C and a max dissipation of 300 watts, will this be adiquit for this amp?


Thanks again,


Opie
  Reply With Quote
Old 28th February 2002, 02:24 AM   #6
Warp Engineer
On Holiday
 
AudioFreak's Avatar
 
Join Date: Oct 2001
Location: Queensland, Australia
It depends on the thermal resistance of the heatsink/s you'll be using, also if you be using mica or similar insulators, the inductive natural of the load etc etc etc. also may i suggest if you have not already purchased those fets that you seriously consider using IRFP244/254/264 instead as they have a bit more headroom on the supply voltage....
  Reply With Quote
Old 1st March 2002, 08:54 AM   #7
diyAudio Member
 
Join Date: May 2001
Location: Bangalore, India
Opie,

Since you mentioned Anthony Holton's N-channel amplifier, I wish to state the following:

I constructed the N-channel amp with 3 pairs of IRFP250s, all matched very closely. I used an on-load voltage of + - 84, set the quiescent as suggested by the designer; heatsinks were over-rated and there was a fan for additional cooling. I built four PCBs and discovered the following:

1. The pre-regulator transistor, 2SC3298(B) gets too hot for the touch and a small heatsink needs to be attached to keep it under limits.

2. The voltage drop across the output resistors are not at all equal despite the matching of MOSFETs for each bank. I used 3 x 1ohms 1watt resistors for each output device.

3. When there is a slight increase in the AC voltage, the output stage fails.

4. I isolated the input stage with Fast Recovery Diodes and had separate decoupling for input and output stages.

5. More numbers of output devices PROBABLY need to be paralleled to keep the dissipation in each of the output devices within their limits as well as to increase output power.

6. I have tried voltages as low as + - 30 volts and have one module working off about 50volt rungs without any problem.

(P.S. I have 3 PCBs which have been damaged due to higher voltage operation.)

You could search the Solid State Forum here to view a picture of the populated PCB which I have posted a week ago.

THE SUGGESTED 70V MIGHT JUST BE THE RIGHT VOLTAGE FOR THE CIRCUIT WITHOUT ANY MODIFICATIONS WHATSOEVER.

The devices you have suggested are better rated that the ones I used, but note the effect of paralleled device capacitance which might make the high frequency roll off much quicker.
__________________
Sam
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
What is power dissipation? geminni Everything Else 7 14th January 2007 08:39 AM
Q about Total power dissipation Bensen Everything Else 8 29th December 2005 11:02 AM
power dissipation darkfenriz Parts 2 14th December 2004 04:08 PM
Need help in calculating power dissipation mclagett Everything Else 3 24th May 2004 11:52 PM
Power dissipation control byteboy Pass Labs 14 16th December 2003 06:30 AM


New To Site? Need Help?

All times are GMT. The time now is 05:20 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2